Illumi is not one of the main antagonists in Hunter x Hunter. He’s more of a sideline disturbance, and whatever he is he’s certainly not one of the good guys.
When he first comes into the story he looks like someone else, but to change his appearance is just one of his talents. He’s a professional assassin, from a family of professional assassins. And I’m humming “he’s just a poor boy, from a poor family” from Queen’s “Bohemian Rhapsody” right now. He kills people, lots of people, and is extremely good at it. He can change his appearance and control other people by placing pins in their brains. More than that, he seems to divide other people into two groups, those that might be killed and immediate family.
And then there is his little brother Killua. Don’t dare to threaten Killua or Illumi will go bonkers. Well, he’s not hesitating to hypnotize his little brother into murdering someone or controlling him like a puppet. Twisted. Loving, in a way, but twisted, like in committable twisted. But he’s somewhat funny and shows a dry sense of humor.Except he might not know that. And cute, well as cute as the slightly crude drawing style in Hunter x Hunter can be. When I first saw him I thought it was a waste to draw him like that and wished that he were done more realistic. Well, I’m not particularly sane either, when it comes to drawn characters. “You do know that they are drawings, right?” one of my sisters said to me once. Of course I said (and crossed my fingers behind my back) since characters I like and really good story settings feel real to me. No, I don’t believe that they are real, I’m not that much of a nutcase, but if you love books, movies and stories and good characters you know what I mean. I won’t say that I would like to meet Illumi in real life, though. And I can’t believe that there are so few good Illumi/Hisoka fanfics (I’ve had a hard time finding even one). In my world there should be a lot more. There is lot of fanart, though, so maybe I just have to look harder.